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SENT BY~FSP&T, LLC, tl2 .11-211- ~ 7:311AM <br />b <br />LITHOLOGY & FACIES <br />• The matrix of Fort Hays limestone beds is biogenic in origin, composed primarily <br />from pelagic coccolith ooze (>90%), planktonic and benthonic foram tests (-5-7%), and <br />mollusc shell debris (-3-5%). More than 75% of the fine-grained matrix has been <br />diagenetically recrystalized into microspar (Schnlle, 1977; Laferriere, 1987). The <br />composition is almost pure calcium carbonate (-95%), with only an average of 5% <br />aragonite, and no dolomite. The limestone beds vary from dazk olive gray to light gray to <br />essentially pure white in color, and usually weather to a creamy white or buff. The shales <br />can be highly calcareous and medium gray in color, to olive black with very little <br />calcazeous material. In Kansas & Nebraska the Fort Hays Member is predominantly a <br />biomicrite, whereas in Colorado and New Mexico its composition more resembles a <br />biomicrosparite (afrer Folk, I962). The entire Fort Hays Mbr is prcdomirrantly a <br />mudstone (afrcr Dunham, 1962), although locally thin horizons (less than 5 cm) within <br />the unit could be described as wackestones {> 10% grains and clasts). These wackestones <br />may represent distal portions of tempestites (tropical storms, with extensive off-shore <br />transport of sediments) and regional bypassisediment starvation surfaces, as a result of <br />climato-eustatic fluctuations. <br />Most of the clastic sediments (quartz, cherC, feldspars) deposited within the <br />seaway were initially derived from the Sevier Uplands to the west (Figure 2); relatively <br />• little sediment was derived from the lowlands bordering [he eastern shoreline- To the <br />west, the Power Niobrara mtertongues with the Mancos Shale, which essentially lacks any <br />pelagic limestone beds. Further to the west, the Mancos intettongues with the Straight <br />Cliffs Formation (predominantly sandstones) and Indianola Group conglomerates, bath <br />very close to the active Sevier Thntst Belt (precursor to the modem Rocky Mountains). <br />To the north the Fort Hays is correlative with the lower Hilliazd and Cody Shales of <br />Wyoming. To the south and east, however, there are no adjacent rocks to the lower <br />Niobrara The Gulf Coast Cretaceotas sequences (e. g, west Texas), over 800 km to the <br />southeast, do contain coeval strata to the Fort Hays (the Atco Member of the Austin <br />Chalk, for example), but high resolution correlation between these two regiops remains to <br />be undertaken. <br />There are presently several fields producing both hydrocarbons and natural gas <br />from the Niobrara Formation, sometimes in direct association with [he Fori Hays <br />(Barlow, 1985). 'fhe Florence, Colorado oilfield is still productive to the present, and has <br />sortie of the oldest continuously-operating oi) wells in the region east of the Mississippi <br />River. Stratigraphieally adjacent units, such as the Codell Sandstone and lower Smoky <br />• 1996 <br />